1. Field of the Invention
The present invention relates to a pilot-controlled electromagnetic valve system in which an electromagnetic valve block is secured to the top of a manifold block of a valve manifold.
2. Description of the Related Art
Japanese Patent Application Unexamined Publication (KOKAI) No. 2002-250463 (patent document 1) discloses a pilot-controlled electromagnetic valve system in which a multiplicity of electromagnetic valve blocks are mounted on a single manifold block (manifold base) in such a manner that each pair of adjacent electromagnetic valve block are joined together, and the electromagnetic valve blocks are secured to the manifold block by using screws. Japanese Patent Application Unexamined Publication (KOKAI) No. 2000-283324 (patent document 2) discloses an electromagnetic valve system in which a necessary number of electromagnetic valve block and manifold block combinations are provided in such a manner that each pair of adjacent combinations are joined together. A screw accommodating recess for allowing coexistence of a screw is formed on a joint surface at each side of each electromagnetic valve block to extend over from the upper end to the lower end of the joint surface. Each electromagnetic valve block is mounted on a manifold block and secured thereto by using a screw.
FIGS. 3A to 3D show an electromagnetic valve block 10 of the conventional valve manifold disclosed in the patent documents 1 and 2. In the valve manifold, two adjacent electromagnetic valve blocks 10 are jointly fastened with a single screw 11 with a view to minimizing the installation pitch of electromagnetic valve blocks 10. For jointly fastening purposes, a screw accommodating recess 13 for allowing coexistence of a screw 11 is formed on a joint surface 12 at each side of each electromagnetic valve block 10. The screw accommodating recess 13 has an approximately arcuate cross-sectional configuration and extends over from the upper end to the lower end of the joint surface 12. In addition, a bearing surface 15 is formed on the top 14 of the electromagnetic valve block 10 at a position adjacent to the screw accommodating recess 13. The bearing surface 15 is where the reverse side of the head of the screw 11 presses against the top 14 of the electromagnetic valve block 10. As shown in FIG. 3A, when a plurality of electromagnetic valve blocks 10 are disposed adjacently to each other, two mutually opposing screw accommodating recesses 13 of two adjacent joint surfaces 12 form an insertion hole 17 for a screw 11A. The screw 11A is inserted through the insertion hole 17, and the distal end of the screw 11A is threaded into a bolt hole (not shown) formed in a manifold block 16 (see FIG. 3C). Consequently, the abutting surface 18 (see FIG. 3D) on the reverse side of the head of the screw 11A presses against the bearing surface 15 of the electromagnetic valve block 10. Thus, the electromagnetic valve block 10 is secured to the manifold block 16. It should be noted that each electromagnetic valve block 10 is provided therein with a main valve (directional control valve), a manual control device, and a pilot valve in the order mentioned from the right-hand side of FIGS. 3A and 3B.
The above-described jointly fastened structure involves the following problem. The bearing surface 15 on the top 14 has an approximately hollow semicircular configuration as shown in FIGS. 3A and 3B. Therefore, when a screw 11 is applied in an insertion hole 17 where two adjacent electromagnetic valve blocks 10 contact each other, the abutting surface 18 of the screw 11 surely presses against the bearing surface 15. However, when only one electromagnetic valve block 10 is secured with a screw 11, or when an electromagnetic valve block 10 at an end of a series of electromagnetic valve blocks constituting a valve manifold is secured with a screw 11, if a strong external force acts rightward as shown in FIG. 3C, the screw 11 is likely to tilt toward the right-hand side where no electromagnetic valve block 10 is present. In such a case, the screw 11 may come off undesirably.